[PATCH] debuginfod: PR27917 - protect against federation loops

[Di Chen]

Hey Frank,

1) moved the XFF check to handle_buildid.
2) replace "livelock" with "deadlock" in the commit message.

- dichen


On Thu, Aug 19, 2021 at 6:55 AM Frank Ch. Eigler <fche@redhat.com> wrote:

> Hi -
>
> > This patch aims to reduce the risk by adding an option to debuginfod
> > that functions kind of like an IP packet's TTL: a limit on the
> > length of XFF: header that debuginfod is willing to process. If
> > X-Forwarded-For: exceeds N hops, it will not delegate a local lookup
> > miss to upstream debuginfods. [...]
>
> Thank you very much!
>
>
> > Commit ab38d167c40c99 causes federation loops for non-existent
> > resources to result in multiple temporary livelocks, each lasting
> > for $DEBUGINFOD_TIMEOUT seconds. [...]
>
> (FWIW, the term "livelock" is not quite right here, try just
> "deadlock".)
>
> The patch looks functional, and thank you also for including the
> docs and test case.  Thorough enough!
>
>
> > @@ -1862,6 +1869,12 @@ handle_buildid (MHD_Connection* conn,
> >    // We couldn't find it in the database.  Last ditch effort
> >    // is to defer to other debuginfo servers.
> >
> > +  // if X-Forwarded-For: exceeds N hops,
> > +  // do not delegate a local lookup miss to upstream debuginfods.
> > +  if (disable_query_server)
> > +    throw reportable_exception(MHD_HTTP_NOT_FOUND, "not found,
> > --forwared-ttl-limit reached \
> > +and will not query the upstream servers");
>
> One part I don't understand is why you added the code to check for XFF
> length into handler_cb(), and then passed the disable_query_server
> result flag to this function.  Was there some reason not to perform
> the XFF comma-counting right here?
>
>
> - FChE
>
>
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